It is advisable to learn the various ways of using the modal auxiliaries without thinking of grammatical moods at the same time. These auxiliaries lack forms (
must has only one form, for example) and the potential mood, as it exists in some languages, is nonexistent in English. However, auxiliaries such as
may and
can can be used to convey thoughts that are expressed using the potential mood in other languages.
It is perfectly possible, though, that in many cases can may be translated into your native language using the indicative mood. Some auxiliaries are used in conditional sentences, some aren't. The subjunctive is normally formed without modal auxiliaries in English but it is possible that you have to translate some modal auxiliaries into your native language in the subjunctive mood.
If you can get a good grammar book, perhaps in your mother tongue, it explains the many uses of these auxiliaries in greater detail.
CB